1. Field of the Invention
The present invention relates to a heat processing apparatus and a heat processing method for performing a heat process for a substrate such as a mask substrate on which for example a resist solution has been coated.
2. Description of the Related Art
When a semiconductor mask is formed in a fabrication process for a semiconductor device, a resist solution is coated on a square mask substrate. With a photo mask, the resist film is exposed and developed. As a result, a desired resist pattern is formed. As such a substrate, for example a six-inch size square glass substrate having four sides each of which is 152 mm long and having a thickness of 6.35 mm is used.
The resist solution is made by dissolving a component of a coating film in a solvent. After the resist solution is coated on a substrate, a heating process for heating the substrate at a predetermined temperature and evaporating the solvent is preformed. The heating process is performed by placing a substrate on a heating plate that has a heater. However, when a substrate has a large thickness as described above, the temperature uniformity of the surface of the substrate tends to deteriorate. In other words, when a substrate has a large thickness, heat radiated from the side surfaces of the substrate is large, therefore, there is a tendency of which the temperature of the peripheral region of the substrate is lower than the temperature of the center region. Thus, when the substrate temperature varies on the surface of the substrate, the evaporation amount of the solvent varies on the surface. As a result, the uniformity of the surface of the resist film deteriorates.
Thus, as shown in FIG. 19, a concave portion 11 is formed in a heating plate 10. A substrate 12 is placed in the concave portion 11. In this state, the substrate 12 is heated by the heating plate 10. As a result, vicinity regions of the side surfaces of the substrate are heated by the heating plate 10. Thus, heat radiation from the side surfaces can be suppressed. In FIG. 19, reference numeral 13 represents a heater. However, in such a method, particles may accumulate at corner portions of the concave portion 11. It is difficult to remove these particles. In addition, there is a possibility particles adhering to the substrate 12. Moreover, to form the concave portion 11 in the heating plate 10, long time and great cost will be required. Thus, the fabrication cost of the substrate will rise.
To suppress heat radiation from the side surfaces of the substrate, the inventors of the present invention are devising a technique of which a side plate 14 is disposed around a substrate 12 placed on a heating plate 10 as shown in FIG. 20. As examples of such a technique, a structure of which an outer frame that is higher than an object to be processed and surrounds the object is disposed at a predetermined placement position of the object on a heating plate (refer to, for example, Japanese Patent Laid-open Publication No. 11-204428 published by Japan Patent Office), a structure of which a side plate that is equal to or higher than a mask and that surrounds it is disposed on a heating plate, and a structure of which a side heating plate disposed around a mask placed on a heating plate prevents heat radiation from side surfaces of the mask (refer to for example Japanese Patent Laid-open Publication No. 2002-100562 published by Japan Patent Office) have been proposed.
However, the publication No. 11-204428 discloses the outer frame so as to prevent air from entering the vicinity of a substrate. Thus, the outer frame is disposed on the heating place without a clearance. Likewise, the publication No. 2002-100562 discloses the structure of which the side plate and the side heating plate are disposed without a clearance as shown in FIG. 4 and FIG. 6 of the publication. Since the outer frame of the publication No. 11-204428 and the side plate of the publication No. 2002-100562 are disposed in such a manner that they are higher than the front surfaces of the object to be processed and the mask. Thus, as shown in FIG. 21, when particles 15 scatter by an air current in a processing vessel and contact the front surface of the substrate 12, the particles 15 may cause a defect of the substrate to be processed. When the particles 15 enter a clearance formed between the substrate and the side plate 14 or the like, the particles 15 do not scatter, but accumulate at corner portions between the side plate 14 or the like and the heating plate 10. As a result, there is a possibility of which the substrate 12 is contaminated by particles 15.